One of the major obstacles that are limiting the development of deployable integrated sensing and actuation solutions in smart structures is the scarcity of power. Several applications require of the use of miniaturized low-powered sensing and actuation systems. These applications include civil and mechanical structures monitoring, machinery/equipment monitoring, home automation, efficient office energy control, surveillance and security, agricultural management, long range asset tracking, and remote patient monitoring. As a result, the power consumption, speed and size of integrated circuits have dramatically decreased. It is now becoming feasible to embed electronics in everyday objects to potentially enhance their performance. For example, a typical wireless sensor node would consist of an embedded microprocessor, digital logic circuits, radio receiver, radio transmitter, timer and an analog-to-digital converter. Current commercial electronics have sleep-power consumptions as low as 200 nW. The processor is capable of 0.5 million operations per second at 350 μW power consumption. Commercial sensor nodes require about 50 mW of power to run the sampling, processing and communication functions. These sensors would typically process and transmit approximately 500 bytes of data per milli-joule of energy. Recently, a data computation and logging system for sensing applications have been reported to achieve data processing and storage at power levels below 1 μW. The actual power consumption in real applications strongly depends on the complexity of the processed signal quantity and on the number of times per second it has to be transmitted. Several recent practical implementations of sensor nodes showed that 20 μW to 100 μW is enough to process and transmit data. The value of 100 μW is considered representative of the latest developments of relatively complex nodes for systems operating at relative high data-rate.
In spite of the significant developments in the area of localized sensing and actuation, most of the developed systems to date still rely on batteries, thus limiting the lifetime of the device as well as the diagnosis possibilities. Therefore, energy harvesting has been a topic given great attention in recent years as a viable alternative. A myriad of potential energy sources have been identified. Among the identified methods, piezoelectric harvesters are the most promising for deployment in structures, given the size limitations and the possibility of being embedded within the construction material.
A major disadvantage that hinders the use of piezoelectric scavengers in most of the civil and mechanical applications is their narrow-band frequency response. For example, FIG. 1 shows the frequency response of a PZT generator of dimensions (40 mm×10 mm×0.5 mm) for both surface mounted and cantilever vibrator configurations (a tip mass of 3 g is attached in vibration mode). FIG. 1 illustrates the importance of frequency matching for an optimized energy delivery. In general, a vibration based scavenger with an overall volume limited to less than 5 cm3 will exhibit a resonant frequency in the range 50-300 Hz, while most civil structures have a fundamental vibration mode at frequencies less than 5 Hz. This mismatch significantly limits the levels of extractable power. Thus, improving the conversion capabilities of these systems, while obeying all necessary constrains, is critical toward a successful implementation of energy harvesting strategies.
This section provides background information related to the present disclosure which is not necessarily prior art.